Four days is a long time in fashion. When I got to New York at the weekend, fashion was having a moment, and not in a good way. It was having a why-are-we-all-here, what's-the-point-of-it-all moment. New York fashion week has just moved from a few marquees in Bryant Park, close to the Seventh Avenue garment district, to the way-more-grand Lincoln Center, home to the ballet and the opera. It's only about 20 blocks north, but it feels very, very different. The subtext seems to be that fashion week is no longer a trade show, but a week-long advertisement for fashion as another branch of culture.

With the umbilical cord to Seventh Avenue cut, the week began with a disorienting, untethered feeling. In the middle of the central hall where show-goers mill between shows, a sunken glass box has been installed for bloggers. It's very white, always very full, and always very brightly lit, which means that non-bloggers stand around mindlessly, gawping into it. It reminds me of the old egg-shaped Lubetkin penguin enclosure at London Zoo, which was conceived as a stage set.

For me, that blogging box represents how fashion feels about the new digital world order. Those young people in there on their laptops are, still, a kind of exotic species. Fashion has come round to the idea that we should be treating this interesting breed with kindness, but it still doesn't feel comfortable around them. Despite being new, the blogging box seems to represent how outmoded fashion can be. I mean, even the penguins were rehoused in a more natural environment years ago.

The thing about fashion shows is that a lot of them are actually really boring; but when they're good, they are brilliant. When you've been watching ho-hum parades of solemn teenagers in underwhelming, overpriced clothes, and then suddenly a designer really pulls it off – at that moment, a fashion show is a joy to behold. It's like watching a sprinter at the top of his game, pulling away from the pack and tearing forward to the finish line: you're watching the race, but for a moment you're there with him, leaving the world in a blur behind you, and it lifts your spirits.

That happened twice this week, at Tom Ford and Marc Jacobs. They were very different evenings: Ford's show for his first own-name womenswear collection, held in his Madison Avenue menswear boutique on Sunday, was self-consciously retro and intimate. It was a blockbuster show scaled down to human size, with enough star power on the celebrity-packed catwalk (Beyoncé, Julianne Moore) to fill several Broadway theatres – and yet, in deliberate contrast, just 100 people invited to a small boutique.

Marc Jacobs, the following evening, was a giant event with guard rails to control the shoving mob outside the doors; an army of black-clad PR people barking into their headsets and manically swooshing fingers across the seating plans on their iPads; and a giant gold-painted circular stage set, of the monumental kind that has become associated with Karl Lagerfeld's shows for Chanel at the Grand Palais in Paris.

Both Ford and Jacobs filled their rooms with excitement. At Ford it was a giggly, this-is-way-too-much-fun-to-be-work kind of excitement. Jacobs pulled off his trick (he doesn't do it every season, but with impressive regularity) of seemingly drilling through the concrete floor of the New York Armoury into a deep vein of that famous Manhattan energy, then pumping it direct on to the catwalk, so that the show takes on a surreal, super-charged intensity you can feel as the audience leave a little louder and more shiny-eyed than they went in.

By then, on Monday night, it felt like we'd come a long way from the week's timid start. At first, it had felt like the spring collections were firmly set on the minimalist path which Phoebe Philo at Céline has carved out for fashion. Alexander Wang did Helmut Lang minimalism in softly layered whites and outmeals, with a dash of grunge in the shredded knits and dungaree shapes: a melange of 90s trends, I guess. White dresses were everywhere. I saw a few more dresses, and dutifully underlined "white dresses" in my notebook. Ho hum.

But then, all of a sudden, things began to pick up. At Victoria Beckham, for the first time I found myself bewitched not just by the shapeliness but by the rich colours of the dresses: a yolky, 60s yellow in cotton waffle and a glorious deep purple silk gazar. ("I love colour for summer," said Mrs B, which I must say surprised me, as I feel like I only ever see her wearing black.)

Downtown at DKNY, I fell in love with an emerald silk blouse tucked into Delft blue shorts. That evening at DVF, we saw the first collection by Diane's new creative director, Yvan Mispelaere, the lovely Nathan Jenden having left to concentrate on his own-name collection. Being Diane's creative director is a bit like being a water-diviner: you have to be able to sense where the DVF feeling is in fashion right now; seek out the right form by which you can help your customers express their inner Diane-ness this season. (DVF is, after all, all about the Diane-ness in us all. How could it not be? She's fabulous.)

A lime-green georgette halter neck silk top, worn with jade bermudas, came down the catwalk and I realised that (although, personally, there is no way I can pull off that colour combination, more's the pity) I do not want white to be the colour of next season. I want colour. I want clothes that conjure up those first days in March when the sunshine turns lemony.

Lucky me, looks like I got it. The colours at Marc Jacobs – peaches, pinks, purples and pumpkins – were 70s YSL, but with the volume turned up so that they were lurid rather than nostalgic. They were the colours of the kind of holiday cocktails that come with a pink umbrella and two straws. Perhaps the Yves Saint Laurent retrospective exhibition that was staged this year in Paris, where Jacobs is based part of the year, fed into these clothes. (Jacobs always breezily admits, with the casual confidence of someone to whom ideas flow free and easy, that he takes fashion influences from the past when it suits him.) But there was also more than a touch of Biba; and – in the kohl eyes, the frizzy hair, and the big hats with the pushed-back brims – a hint of Jodie Foster in Taxi Driver.

Tom Ford's collection was more a celebration of individual beauty than a themed show, but there was a strong seam of 70s-era YSL running through it. There was a slick trouser suit in bleached-out leopardprint, a safari jacket in chalk-white suede, and Daria Werbowy was slinky in a bronze lurex cocktail dress. The hair and makeup – from Beyoncé's fabulous halo of curls to Rachel Feinstein's giant flower corsage to Julianne Moore's exaggerated chignon – had a touch of Guy Bourdin's fashion-noir.

The arithmetic of fashion is never so simple as to be able to say: spring/summer 2011 = 1978, or 1979. There were hints of the 20s and 30s at Tom Ford, as there were at Donna Karan (sublime liquid-gold backless evening gowns) and DVF (simple flapper-style dresses with luxe embroidery). All we know so far is that the 70s mood is out there – Marios Schwab's Halston collection felt like it moved closer to that iconic period of Halston history, for instance, and that Andy Warhol seemed to crop up in conversation throughout the week. But just for now, you might want to hold off with the crimpers and the glitter kohl. With London, Milan and Paris still to go, the fashion finish line is a long way off yet.